It is well established that x- or gamma-irradiation of eukaryotic cells temporarily delays their progression through the cell cycle. Most of the delay occurs in G2 near the point at which the last proteins needed for mitosis are being synthesized. Additional protein synthesis is required for recovery from the G2 block. Recent work has shown that nonhistone chromosomal proteins are synthesized during G2 and are intimately involved with histones in making the structure of the mitotic chromosomes. It is the purpose of this proposal to examine any x- radiation effects on chromosomal proteins. Also such effects will be examined in terms of the factors which influence the duration of mitotic delay such as radiation dose and cell cycle position at the time of irradiation. The possible radiation induced turnover of pre-existing chromosomal proteins and interference with the pattern of chemical modification of chromosomal proteins will be investigated.